There were complaints last year after Jantjie interpreted the proceedings at the ruling African National Congress elective conference, the institute's chairman, Johan Blaauw, told the South African Press Association.

Fake sign language interpreter outrage

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But Jantjie stands by his work. "I have never in my life had anything that said I have interpreted wrong," he said.

"For the deaf association, if they think that I have done a wrong interpretation, I ask forgiveness. For Deaf SA, if they are telling me that I was doing a wrong interpretation, then they should answer me why they were silent all the time, all these years," he said, referring to the Deaf Federation of South Africa, which has criticized his work at the service.

Jantjie declined to provide details about his hire for the four-hour memorial, watched by millions around the world, as a government inquiry looks into the matter.

He said he had been drawn to the job of interpreting because he was disabled.

"I am suffering from schizophrenia, which is controllable. I am under treatment," Jantjie said.

At a news conference Thursday, Hendrietta Bogopane-Zulu, South Africa's deputy minister of women, children and people with disabilities, admitted that mistakes had happened at the memorial service but added that Jantjie was not a "fake."

She said there was no sign language standard in South Africa and deaf people spoke different dialects.

She added that the government was looking into the vetting of Jantjie's security clearance at the memorial.

"But normally when you do provide a service at a particular level, you will be vetted. And as you could see, he had his accreditation, so he didn't just walk through," she said.

Bogopane-Zulu also said the government tracked down the company Jantjie worked for, but the owners "seemed to have vanished."

"We managed to get hold of them and then we spoke to them, wanting some answers, and they vanished into thin air," she said. "They have been providing substandard service for years."

Jantjie named his employer as a company called SA Interpreters. He did not give details about his training, saying his qualifications are filed with the company.

"You can look at my portfolio, it speaks for itself from the events that I have done in my country," he said.

As outrage over his interpretation skills have grown, so have questions about who hired him.

The ANC said it did not hire Jantjie for the service, as it was the state that had organized the memorial.

"The processes that were followed to procure Mr. Jantjie's services were thus government processes and not ANC processes," the ruling party said in a prepared statement, adding that it had used his services before.

"It is important to make the point that, up until yesterday, the African National Congress had not been aware of any of complaints regarding the quality of services, qualifications or reported illnesses of Mr Jantjie."